Hair appears in many places on the human body. For cosmetic reasons, frequently individuals wish to remove the hair from certain body areas. Hair removal may be temporary, as for example through shaving, or permanent. Permanent hair removal requires destruction of the hair follicle itself; from which the hair grows. Each hair follicle is located in the dermis. The hair grows from the bottom of the hair follicle, from a location known as the dermal papilla. Without wishing to be limited by a single hypothesis, it is believed that the cells of the papilla must be destroyed in order to prevent the hair from growing back. However, its location in the lower dermis makes it more difficult to destroy without also destroying the skin tissue above and to the sides of the papilla. It has also been stated that hair growth is controlled by the bulge in the follicle that is typically located in the middle dermis; however, regardless of the location of the cells which control or promote hair growth, it is still necessary to penetrate deep enough into the skin to cause permanent hair (and tissue) damage.
Many different devices are available for hair removal by destroying the hair follicle. These devices generally suffer from a number of drawbacks. First, many such devices tend to cause damage to surrounding tissue. Second these devices are frequently difficult to apply optimally to destroy the hair follicle while still minimizing damage to surrounding tissue. As a result, a less skilled user can cause severe damage to the skin, for example by causing burns. The problem is particularly acute in that many devices rely upon electricity to destroy the hair follicle, which can easily also cause damage to surrounding tissues.
One example of such a device features a needle inserted into the hair follicle itself. High frequency electrical waves are then applied to the needle in an effort to destroy the hair producing papilla area. These types of devices are illustrated in U.S. Pat. Nos. 3,054,405 and 2,894,512. The insertion of the needle under the skin causes damage in various ways, as the needle itself causes irritation and swelling, while the application of electricity causes burning of the tissues. Also, needle based hair removal devices are limited by the speed of treatment. Since accurate insertion of the needle is critical in order to avoid unwanted damage to healthy tissue and to assure permanent damage to the hair follicle, it is very important that the operator be very accurate each time that the operator inserts the needle into the skin. This makes the electrolysis process lengthy, tedious and prone to human errors.
Other hair removal devices use an electrically charged tweezer which grips the hair above the skin and to which high frequency electrical waves are directly applied, such that the hair itself becomes a conductor to conduct electricity directly to the follicle. Such devices are shown in U.S. Pat. Nos. 4,174,713 and 5,026,369. Since this device does not use a needle, damage caused by the needle itself is avoided. However, this type of device is based on the assumption that hair conductivity is high enough to assure that electrical current reaches the hair follicle. In reality, human hair has a very high resistance and thus the electrical energy may not reach the hair follicle and destroy it to permanently block hair re-growth. Also, as this device requires the application of a strong electrical current near the skin, improper use of the device (by allowing the tweezer tip to contact the skin surface) may cause severe burns to surrounding skin tissue. Furthermore, the device must be applied separately to each hair, which is a painstaking and lengthy process, particularly for large areas of skin.
Other devices rely upon direct contact with the skin, but use some type of conductive lotion to guide electricity only to the hair follicle. Again, the hair itself is used a conductor, such that electricity is conducted down the hair to reach the hair follicle and destroy it. One example of such a device is disclosed in U.S. Pat. No. 5,522,814, which requires application of a conductive lotion. The lotion penetrates the pores of the skin and assists conduction of electricity to the hair follicle. However, this device still suffers from the drawbacks of the devices described above, in that electricity has to be conducted by the hair to the follicle, which, as noted above, is not very effective, due to the high resistance of hair. Furthermore, it may also easily cause damage to the surrounding skin, since current cannot be precisely pinpointed only to the hair follicle.
Even devices which attempt to treat only very small areas of the skin, such as those disclosed in U.S. Pat. No. 5,534,003, cannot pinpoint the hair follicle for treatment with electrical current, and hence cannot avoid damage to the surrounding skin tissue.
Other devices attempt to avoid any direct application of current to the skin, by using heated filaments located near the skin which burns the hair. For example, U.S. Pat. No. 2,727,132 discloses a device which features a heated filament and a skin guard to prevent contact between the filament and the skin, while still permitting the hair itself to be burnt. These devices may be configured so as to raise the heated filament away from the skin, thereby reducing the danger of burning the skin. However, they are not effective at destroying the hair follicle and hair re-growth can easily occur.